I am looking to identify the short sci fi story described below. It may be a really commonly known one, I just cannot remember the author or title.

A spaceship lands on a planet that is largely unexplored. A team of humans go in to investigate. They climb some trees, but these turn out to be huge tripedal worms, basically three large legs attached at a central hub. The human team accidentally (?) kill the juvenile worm, leading the parent worm to attack them. The last surviving member of the team starts running towards the spaceship, which is set to automatically leave the planet at a certain time. The worm pursues him by spinning around its centre like a wheel, each leg rising up and over before hitting the ground. The ship leaves before the human can reach it.

The story ends with the human and the worm in an endurance race, where it is implied that if the human tires before the worm, he will be crushed. The human says to the alien something like: 'thou art mighty', with the alien replying something like 'thou art mightier than I'.

I may have a few details wrong: i.e. maybe the worms have 4 'legs'. It's been many years since I read it.

There was a motion in the bush ahead. A large body was moving through the thicket, just out of sight, coming toward them. A serpentine neck poked out of the copse, bearing a cactuslike head a foot in diameter. The head swung toward them, circularly machairodont, a ring of six-inch eye-stalks extended.

The men froze, watching the creature. The head moved away, apparently losing its orientation in the silence. The neck was smooth and flexible, about ten feet in length; the body remained out of sight.

Immediately the head reacted, demonstrating acute hearing. It came forward rapidly, twenty feet above the ground; and in a moment the rest of the creature came into sight. The body was a globular mass about four feet across, mounted on a number of spindly legs. The creature walked with a peculiar caterpillar ripple, one ten-foot leg swinging around the body in a clockwise direction while the others were stationary, reminding Tinnerman of a wounded daddy-long-legs. The body spun, rotating with the legs; but the feet managed to make a kind of precessional progress. The spin did not appear to interfere with balance or orientation; the ring of eye-stalks kept all horizons covered.

Here is the ending:

Eleven hours later, on schedule, the ship took off. It would be three, four, five years before a squat colony ship came to set up frontier operations.

Quink was stalking him with ageless determination and rapidly increasing sagacity. Already she had learned to anticipate the geometric patterns he traced. He had led her through a simple square, triangle and star, giving up each figure when she solved it and set her body to intercept him ahead. Soon she would come to the conclusion that her prey was something more than a vicious rodent. Once she realized that she was dealing with intelligence, communication could begin.

Perhaps in time she would forgive him for the death of her child, and know that vengeance had been doubly extracted already. The time might come when he could walk in the open once more and not be afraid of a foot. At night, while she slept, he was safe; but by day—

Perhaps, when the colonists came, they would be greeted by a man riding the mightiest steed of all time. Or by the quinquepedalian, carrying its pet. It did not matter who was ascendant, so long as the liaison was established.

"Creature of the forest," he said again, doubling back as he perceived her bulk in wait at an intersection of the triquetra pattern. For a moment he stood and looked at her, so vast and beautiful, spinning in the dance of his destruction. "Creature of the forest," he said, "Thou art mighty.

"Thou art mightier than I." There was an answering blast bels in magnitude, like a goddess awakening beyond the horizon.

Seems to me it was the man, not the alien, saying "Thou art mightier than I."